The present invention relates generally to a light-emitting diode (“LED”) lamp device using a plurality of LED elements. More particularly, the present invention relates to an LED lamp device having a fluorescent element disposed about a plurality of LED elements and shaped or formed so as to emit light of substantially uniform color.
LED lamp devices such as shown in FIG. 6, and as conventionally known in the art, may generally have a plurality of LED elements 20 mounted on a mounting substrate 10 for improved luminous intensity. The LED elements 20 are covered without any intervening space by a fluorescent element 30 formed of a translucent material containing or otherwise dispersed with a fluorescent material. In particular, an LED lamp device which uses a blue LED (i.e., an LED element effective to emit “blue” light in a short-wavelength range) and which uses a fluorescent element effective to convert blue light radiated from the blue LED into yellow light has been found to be useful as a white light source.
However, in the conventional example described above, the fluorescent element 30 is formed in such a manner that a thickness of a light-emitting unit 50 including the LED elements 20 and the fluorescent element 30 becomes uniform without depending on a location of the LED elements, thus causing color unevenness. Specifically, comparison of light path lengths of blue light B1 to B3 (see FIG. 6) radiated from the blue LED element 20 until it is radiated to outside of the fluorescent element 30 shows that the light path length of B1 or B3 radiated laterally with respect to the LED element 20 (or more particularly with respect to the surface of the substrate) is relatively long, while the light path length of B2 radiated outwardly with respect to the LED element 20 (or more particularly with respect to the substrate) in the figure is relatively short. The proportion of light radiated thereby from the LED element 20 and then converted into yellow light depends on a light path length of this light until it is radiated to the outside of the fluorescent element 30. Therefore, for light radiated from immediately above the LED element 20, the proportion of the converted light is small and thus a ratio of blue light is large, while for light radiated from a peripheral edge portion of the fluorescent element 30 or a space portion between the LED elements 20 the proportion of the converted light is large and thus a ratio of yellow light is large. This may produce a color difference (color unevenness) depending on a location with respect to the light-emitting unit 50.
An LED lamp device as previously known in the art (and as shown for example in FIG. 7) may seek to address this problem by providing a fluorescent material sheet 31 which is disposed along the top surfaces of a plurality of LED elements 20 mounted with a space there-between, and which has grooved sections 44 individually formed at regions covering the spaces between the LED elements 20. An adhesive agent 21 may be provided between the sheet 31 and the LED elements 20. A light path length of light (B1) radiated from the top surface of the LED element 20 toward the grooved section 44 and outside of the fluorescent material sheet 31 is shorter than that of the example previously described and as shown in FIG. 6, and is substantially equal to a light path length of light (B2) radiated from the top surface of the LED element 20 directly outward and to the outside of the fluorescent body sheet 31. Thus, the ratio of blue light and yellow light becomes substantially uniform without depending on a location along a surface of the fluorescent material sheet 31, which can therefore suppress color unevenness.
However, in the example shown in FIG. 7, the top surfaces of the LED elements 20 are merely covered by the sheet-like fluorescent material sheet 31, thus forming an air layer 22 between the LED elements 20. Thus, there is a risk that part of the light emitted from a side surface of the LED element 20 is lost as a result of being subjected to, for example, multiple reflections between the side surfaces of the LED elements 20, and generally resulting in reduced luminous efficiency.